In recent years, attention has been attracted by ultra-wide band (UWB) type communication using a short pulse signal. In the technique, a short-width pulse is used to obtain spread spectrum, thereby suppressing transmission power per unit frequency and enabling coexistence with other signals. The UWB technique has been vigorously researched and developed mainly in the field of short-distance wireless transmission, and started to be studied partly in the field of wired or optical transmission.
Patent Document 1 describes a demodulation device which demodulates a short-pulse signal used in the UWB technique. FIG. 14 is a diagram illustrating a configuration of the conventional demodulation device described in Patent Document 1. FIG. 15 is a diagram illustrating waveforms of signals output from major sections of the demodulation device of FIG. 14. Note that (a) to (c) and (e) illustrated in FIG. 14 indicate that signals illustrated with (a) to (c) and (e) of FIG. 15 are output in directions indicated with arrows, respectively.
The demodulation device 300 of FIG. 14 is wirelessly connected to a transmission device (not shown), and demodulates a wireless signal transmitted from the transmission device. The demodulation device 300 includes a correlation section 320, a template signal generating section 340, a synchronization section 350.
The demodulation device 300 inputs a received wireless signal as a received signal into the correlation section 320. FIG. 15(a) is a diagram illustrating a waveform of the received signal (short-pulse signal) input to the correlation section 320.
The template signal generating section 340 generates a template signal based on a synchronization signal output from the synchronization section 350 (described below) and a hopping pattern, and outputs the template signal to the correlation section 320. The hopping pattern is a pattern, such as that illustrated in FIG. 15(b), which indicates timings with which pulses to be received are present.
FIG. 15(c) is a diagram illustrating a waveform of the template signal output from the template signal generating section 340. The template signal is a signal which has a waveform similar to that of the received signal and is in synchronized with the received signal.
The correlation section 320 obtains a correlation value between the waveform of the received signal and the waveform of the template signal to demodulate the received signal, and outputs the received signal as received data. FIG. 15(d) is a diagram illustrating the correlation value obtained by the correlation section 320. FIG. 15(e) is a diagram illustrating the received data output from the correlation section 320.
When the obtained correlation value is larger than or equal to a positive threshold value (e.g., 0.5), the correlation section 320 identifies data “1”. On the other hand, when the obtained correlation value is smaller than or equal to a negative threshold value (e.g., −0.5), the correlation section 320 identifies data “0”. When the obtained correlation value is neither larger than or equal to the positive threshold value nor smaller than or equal to the negative threshold value, the correlation section 320 identifies that there is not a pulse. For example, when the waveform of the received signal completely matches the waveform of the template signal, the correlation value obtained by the correlation section 320 is +1. On the other hand, the waveform of the received signal and the waveform of the template signal have phases completely reverse to each other, the correlation value obtained by the correlation section 320 is −1.
The synchronization section 350 outputs a synchronization signal which is in synchronization with the received signal, to the template signal generating section 340. Also, the synchronization section 350 adjusts the phase of the synchronization signal so that the correlation value in the case of data “1” is maximized.
Note that, typically, in order to effectively obtain spread spectrum, time hopping is performed in which a pulse position within a bit cycle is changed per bit based on a pseudo-random pattern. However, in FIG. 15, for the sake of simplicity, the pulse position within the bit cycle is assumed to be fixed.
As described above, the demodulation device can demodulate a short-pulse signal received wirelessly, by obtaining a correlation value between a received signal and a template signal.
Patent Document 1: Japanese National Phase PCT Laid-Open Publication No. 11-504480